There are a multiplicity of sources for crude caprolactam like wastewater from the manufacture and thermoplastic processing of polycaprolactam (nylon 6) or catalytic cracking of oligomers and polymers of caprolactam.
Extractions of wastewater from the manufacture of polycaprolactam contain oligomers, polymers and monomers of epsilon caprolactam, are hereinafter referred to as caprolactam. There are several methods known for the recovery of caprolactam from these extractions, which contain oligomers and polymers of caprolactam. DE-A 950,726 and DE-A 1,272,287 disclose a depolymerization of polycaprolactam with phosphoric acid. The crude caprolactam is distilled by a steam distillation. The distilled caprolactam does not meet all quality requirements and the phosphoric acid containing residues are difficult to dispose.
DD-A 5310 discloses a depolymerization of polycaprolactam with sodium hydroxide.
U.S. Pat. No. 5,169,870 discloses a process for the recovery of epsilon caprolactam from nylon 6 carpet by catalytical depolymerization of the polycaprolactam, followed by vacuum distillation.
Object of the present invention was to provide a process for the purification of crude caprolactam which produces caprolactam in high purity and yield.